var items = [
    {
        id: 1,
        title: '项目1',
        children: [
            {
                id: 11,
                title: '项目1-1'
            }, {
                id: 12,
                title: '项目1-2'
            }, {
                id: 13,
                title: '项目1-3'
            }
        ]
    }, {
        id: 2,
        title: '项目2',
        children: [
            {
                id: 21,
                title: '项目2-1'
            }, {
                id: 22,
                title: '项目2-2'
            }
        ]
    }
]
